Photodetectors convert electromagnetic radiation, such as visible and infrared light, into an electronic signal that is proportional to the incident electromagnetic radiation. Photodetectors based on interband transitions in bulk materials or quantum wells generally operate in the visible and near infrared wavelengths. Photodetectors based on intersubband transitions in superlattices, quantum wells, or quantum dots generally operate in the infrared wavelengths.
A quantum well infrared photodetector (QWIP) is a device that produces intersubband transitions within a conduction band (or valence band) of a semiconductor material when a ground state electron moves to an excited state upon absorbing an incident photon having energy equal to the subband spacing. In the excited state, the electron can move freely within the QWIP to cause an electrical current under bias. Conventional QWIPs generally consist of multiple layers of compound semiconductor materials, for example, alternating layers of InGaAs and AlGaAs, between two contact layers.
A conventional quantum dot infrared photodetector (QDIP) generally consists of one or more layers of quantum dots between two contact layers. The quantum dots have a size approximately equal to the wavelength of an electron in the crystal structure and act as a localized attractive potential (potential hole). Because the electrons are confined to the hole, they have discrete energy levels similar to the energy levels of an atom. Thus, the quantum dots can be made to be sensitive to particular wavelengths of light by controlling the size and potential of the quantum dots. If an incident photon has a wavelength corresponding to the separation of the ground and the excited state, it can be absorbed. An electric field can be applied to the quantum dots to remove the excited electrons. The change in electric current, which is proportional to the intensity of light, can then be measured.
Conventional photodiodes, however, suffer from low responsivity and low quantum efficiency. Additional problems arise due to the low operating temperatures of these devices.
Thus, there is a need to overcome these and other problems of the prior art to provide devices and methods for detecting electromagnetic radiation that have increased quantum efficiency and higher operating temperatures.